1. Field of the Invention
The present invention relates to vehicle detecting systems, and more particularly, to a vehicle detecting system including an image taking means that takes images for detecting at least a vehicle.
2. Description of the Related Art
In recent years, techniques of detecting objects existing around a vehicle, such as a car, by analyzing an image taken by an image taking means, such as a charge coupled device (CCD) camera, or analyzing reflected waves of radio waves emitted from a radar apparatus, have been developed (for example, see Japanese Unexamined Patent Application Publication No. 2006-140636). These techniques are applied to safe driving technologies for vehicles. For safe driving, for example, the probability of a collision with a detected object is judged, an alarm is given to alert the driver, and automatic steering and automatic brake control are exerted in order to avoid the collision.
In this object detection, it is important to accurately detect the positions of other vehicles, particularly, a preceding vehicle. It is also important to accurately detect not only the distance in the front-rear direction between a subject vehicle and a preceding vehicle, but also the position of the preceding vehicle in the lateral direction (hereinafter referred to as a lateral position) in order to judge the probability of a contact or a collision with an object.
In this respect, the above-described detection technique using the radar apparatus can, in general, accurately obtain the distance in the front-rear direction, but cannot easily increase the accuracy in detecting the lateral position. In contrast, the above-described image analysis of a taken image provides a high accuracy in detecting the lateral position because of the capability of accurately detecting the shape of the vehicle. However, since the image is taken in pixels, the accuracy of data on the distance from the subject vehicle particularly to a remote vehicle sometimes decreases.
In order to utilize the advantages of the detection techniques using the radar apparatus and image analysis of the taken image and to overcome the disadvantages of the techniques, the above-described publication proposes a detection system using a radar and image analysis in combination. In this detection system, a rough position of, for example, a preceding vehicle is detected as a region to be processed by the radar, multiple histograms are calculated by detecting edges in the region by an image taking means, and the lateral position of the preceding vehicle are detected by following the preceding vehicle with reference to the stored histograms.
Unfortunately, in the above-described detection system, it is necessary to calculate multiple histograms and to store large amounts of data. Moreover, since it is necessary to extract values that have time continuity from the data, much time is taken for processing, in other words, processing becomes slow.
Once a wrong position is stored, it is not necessarily easy to correct the position to a right position. When the brightness pattern of a preceding vehicle or the like changes with time and place, stability of the processing result is not necessarily ensured effectively.
It is conceivable to estimate the lateral position of the preceding vehicle on the basis of only histograms to which lateral edges of the preceding vehicle are added, without checking against the stored data. However, for example, when the preceding vehicle runs past an object whose edges are dense, such as the bush, more edges exist in the bush than in the preceding vehicle, and therefore, it is difficult to accurately detect lateral ends of the preceding vehicle.